Complexes of palladium and of triphenylphosphine have been known for a very long time. For example, the preparation and the use of complexes based on palladium and triphenylphosphine are described by Heck in U.S. Pat. Nos. 3,960,932 and 3,988,358. These complexes permit carbonylation reactions of aromatic bromo or iodo compounds, but do not permit in any circumstance the carbonylation of chlorinated aromatic compounds.
When one skilled in the art, reading the prior art, attempted to carbonylate aromatic compounds in a homogeneous medium, it was always necessary to start with aromatic bromo or iodo compounds and then to complex them with a complex palladium salt. It has also been known for a very long time that brominated aromatic compounds are much more costly in price than chlorinated compounds. The problem of carbonylation of chlorinated aromatic compounds is a problem which the present invention has attempted to solve.